616 CIRCULATION OF BLOOD AND LYMPH. 



be affected independently by stimulation of the third, fourth, 

 and fifth thoracic spinal nerves, and hence concluded that 

 these nerves contain vasoconstrictor fibers to the pulmonary 

 vessels, the course of the fibers being, in general, that taken 

 by the accelerator fibers to the heart, namely, to the first 

 thoracic sympathetic ganglion by the rami communicantes and 

 thence to the pulmonary plexus. They give evidence to show 

 that these fibers are stimulated during asphyxia. The authors 

 state, however, that the effects obtained upon the pressure in the 

 pulmonary artery are relatively and absolutely small as compared 

 with the vasomotor effects in the aortic system. Similar results 

 have been obtained by other observers (Frangois-Franck). Using 

 another and more direct method, Brodie and Dixon* have come 

 to an opposite conclusion. These authors maintained an artificial 

 circulation through the lungs and measured the rate of outflow 

 when the nerves supplying the lungs were stimulated. Under these 

 conditions stimulation of the vagus or the sympathetic caused no 

 definite change in the rate of flow, — a result which would indicate 

 that neither nerve conveys vasomotor fibers to the lung vessels. 

 This conclusion was strengthened by the fact that in similar per- 

 fusions made upon other organs (intestines) vasomotor effects were 

 easily demonstrated. Moreover, epinephrin, pilocarpin, and mus- 

 carin cause marked vasoconstriction when irrigated through the 

 intestine, but have no such effect upon the vessels in the lungs. 

 These authors conclude that the lung vessels have no vasomotor 

 nerves at lili, and their experimental evidence might be accepted 

 as satisfactory^ except for the fact that a similar method in the 

 hands of another observer has given opposite results. Plumierf 

 finds that the outflow through a perfused lung is diminished in 

 some cases by stimulation of the sympathetic branches to the lungs, 

 and also by the use of epinephrin. Under such conditions it is 

 necessary to defer a decision until more experiments are reported. 

 Regarding the vasomotors of the lungs, one can only say, as in the 

 case of the heart, that their existence has not been demonstrated. 



The Circulation in the Brain and Its Regulation. — ^The 

 question of the existence of vasomotor nerves to the brain brings 

 up necessarily the larger question of the special characteristics of 

 the cranial circulation. The brain is contained in a rigid box so 

 that its free expansion or contraction with variations in the amount 

 of blood can not take place as in other organs and we have to con- 

 sider in how far tliis fact modifies its circulation. 



The Arterial Supply of the Brain. — ^The brain is supplied through 

 the two internal carotids and the two vertebrals, which together 

 form the circle of Willis. It will be remembered also that the 



* Brodie and Dixon, "Journal of Physiology," 30, 476, 1904. 

 I Plumier, "Journal de physiologie et de pathologie generale," 6, 665, 

 1904; see also Wiggers, "Jour, of Pharmacol, and Exper. Therap.," 1, 341, 1909. 



